Possible Clues:

• Persistent multifaceted problem
• Marine creature in fine fettle, flipping all but head
• Hercules slew it
• A many-headed serpent in Greek mythology
• Mythological water-monster
• Multi-headed monster slain by Hercules
• Evil alter ego contracted artist ... monster!
• Hercules' serpent adversary
• S.H.I.E.L.D.'s enemy, in Marvel comics
• Mythical many-headed snake